Minimum required prophecy version is incompatible with object (return) type declarations
Recent changes like https://review.typo3.org/c/59600/ introduced
object return type decarations which are only supported as of prophecy version 1.7.5.
This caused nightly, composer minimum builds, to fail: https://bamboo.typo3.com/browse/CORE-GTN-UT2PHP72-646
Therefore the default minimum – as required by phpunit (^1.7) – needs to be raised to 1.7.5.